1. Field of the Invention
The present invention relates to small, flat transformers to be mounted on a printed circuit board or the like. More specifically, the invention relates to a transformer suitable for use in the liquid-crystal back-light power supply system.
2. Description of the Prior Art
The inventor has known a transformer, as shown in FIG. 5, for use in the back-light power supply system. FIG. 5 (A) is a plan view of the transformer; FIG. 5 (B) is a sectional view taken along the line B--B of FIG. 5 (A) in the arrow direction; and FIG. 5 (C) is an electrical circuit diagram of the transformer.
A magnetic core 52 of a conventional transformer 51 is equipped with a left segment 53 and a right segment 54 both formed in section into a laid-down T shape. A bobbin 55 is fitted to the magnetic core 52 at its inner portion 52a. A first winding coil 61 and a second winding coil 62 are wound around one of a plurality of sections of the bobbin 55. Further, third winding coil 63 are wound around the remaining sections of the bobbin 55. In mounting the above-described transformer 51 onto a back-light power supply PCB (printed circuit board), which is not shown, a plurality of lead terminals 65 are previously bent at right angles, the bending ends of the terminals are each inserted into a connecting hole of the PCB, and thereafter the bending ends are soldered.
The aforementioned prior-art transformer has the following problems.
With a recent tendency of downsizing electronic equipment, the diameter of liquid-crystal oriented back-light lamps is being increasingly changed from conventional 4.5 mm (approx. 0.18 inch) to 2.5 mm (approx. 0.1 inch). Along with such a change, there has arisen a strong demand for setting the thickness of the above transformers to be used in the back-light power supply system to 2.5 mm, equal to the foregoing, or less than that.
However, thickness G of the conventional transformer 51 is the sum of thickness D of the inner portion 52a of the magnetic core 52, two times winding thickness E of each winding coil 61 or 62 or 63, and two times wall thickness F of the bobbin 55. It is of great difficulty to make these sizes D, E, and F smaller than as they are, which has accounted for the fact that it has been impossible to reduce the thickness G of the transformer 51 to less than 4.5 mm.